Aspects of the present invention are directed to methods of forming compound semiconductors and, more particularly, methods of forming compound semiconductors on silicon.
Silicon is the second most abundant element on earth and therefore also the cheapest choice for the semiconductor industry. As such, the entire electronics industry is largely dependent on silicon for various applications although, in some, it would actually be preferable to use other materials, such as III/V or II/VI semiconductor materials. III/V or II/VI semiconductor materials often offer superior properties and device performance as compared to silicon and so are better suited for use in certain types of devices. For example, light emitting devices, such as lasers diodes, use a direct bandgap semiconductor and are, therefore, commercially fabricated using gallium arsenide (GaAs) or indium phosphide (InP). Silicon has an indirect bandgap and is, therefore, not suited for lasers. Unfortunately, these III/V or II/VI materials are often very expensive and rare. Indeed, a 2″ sample of silicon may cost approximately 10 EUR whereas a 2″ sample of a III/V semiconductor, such as gallium arsenide (GaAs) or indium arsenide (InAs), may cost approximately 100-400 EUR.
As a solution to the problem of cost and material availability, there have been many attempts at growing, for example, III/V semiconductor materials on top of silicon wafers to build large scale wafers of silicon and III/V semiconductor materials. These methods often rely on thick buffer layers, such as thick defective layers, which are in their own right expensive, to relax the lattice mismatch between silicon and the III/V semiconductor material. Even with such buffer layers, typically, several micrometers of different III/V semiconductor materials must be grown before enough defects (mainly misfit dislocations) nucleate to effectively relax the films.
Attempts to mitigate these problems have previously relied on trapping dislocations by forming trenches in the silicon, in which other semiconductor materials are made to grow, whereby defects or dislocations get trapped as they hit the trench sidewalls. Here, a further issue is that, as the trenches are overgrown, still new defects form as additional films form on top of the trench walls.